On Feb. 10, NASA’s Pluto-bound New Horizons probe entered the homestretch of its mission.
When you are sprinting across the solar system, “homestretch” is the final 1 billion miles of your journey. That sounds like quite a stretch, but the half-ton spacecraft has already logged 2 billion miles since its launch in early 2006. That’s twice the distance between Earth and Saturn.
Though the spacecraft is still three years away from its Plutonian close encounter, mission scientists call this the Late Cruise phase of the flight.
The nuclear-powered probe will zoom by Pluto and its moons, possibly navigating a hazardous ring system on July 14, 2015.
Even if the space traveler had artificial intelligence (as its distant descendants will), it would still be unaware of crossing this milepost — the spacecraft’s electronics are in hibernation. Controllers at The Johns Hopkins University Applied Physics Lab in Laurel, Md., will awaken the onboard computer in late April for a two-month-long systems and instruments checkout.
Flight engineers will conduct a 24-hour-long near-encounter rehearsal to exercise the spacecraft. During this test, New Horizons will make every maneuver, every instrument scan, and every observation that it actually will do around closest approach in 2015.
Housekeeping chores also include checking out each of the seven scientific instruments, updating software to the onboard command and control computer, and removing a bug that occasionally causes it to reset. (Presently it takes nearly three hours for radio commands from Earth to travel at the speed-of-light to the probe. New Horizons can’t just call tech support!)
At the spacecraft’s present distance, much of the solar system fits within a panoramic field of view.
The sun is reduced to a bright dot seen against the backdrop of constellations, midway between Gemini and Orion. The sun is glowing at one four-hundredth its brightness as seen from Earth. The inner planets are clustered near the sun within an angular diameter equivalent to eight moon diameters. Jupiter appears as a bright star 10 degrees to the west of the sun. Saturn looks like another bright star 25 degrees to the east of the sun.
The fastest manmade object ever built, New Horizons covers nearly a million miles of space each day. Blazing out of the sun’s gravitational well at 34,000 miles per hour, the probe could travel from Earth to the moon in just six hours.
In October 2013, New Horizons will be just 500 million miles from Pluto. In March 2015, that distance will shrink to the Earth-sun separation of 93 million miles. Fully awake, New Horizons will train its cameras on the fast0approaching planetary target.
This will complete a five-decade-long initial reconnaissance of the solar system. And, I predict, the stunning views of the remote world will return Pluto to full planetary status in the public mind.